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Editor Work2016 Vol. 5, No. 6
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2016, 5(6): 559-595.
Abstract
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The application performance of Synthetic Aperture Radar (SAR) instruments is generally limited in their capability to acquire radar images with both high-resolution and wide swath coverage.The available swath width of Polarimetric SAR (PolSAR) systems is even more restricted.Recently, a new PolSAR architecture called the Hybrid-Polarity (HP) architecture has attracted worldwide attentions.Compared with conventional linearly-polarized PolSARs, HP architecture based PolSARs have significant advantages such as wider swath coverage and lower hardware requirement.In this paper, the principles of the HP architecture, including system designs, system models and calibration methods are first reviewed.Two implementation difficulties of the HP architecture, concerning calibration issue and transmit configuration are illustrated.In order to overcome these problems, an improved version of the HP architecture is proposed.A prototype system based on this improved HP architecture developed for experimental validation is also introduced.In the latter part of this paper, applications suitable for the HP architecture based PolSARs are reviewed.Since the quadrature-polarimetric (quad-pol) data provided by an HP architecture based PolSAR system may be directly transformed into conventional linearly-polarized quad-pol data, this part of review is mainly focused on the corresponding dual-pol applications, i.e.Compact Polarimetry (CP) applications.
The application performance of Synthetic Aperture Radar (SAR) instruments is generally limited in their capability to acquire radar images with both high-resolution and wide swath coverage.The available swath width of Polarimetric SAR (PolSAR) systems is even more restricted.Recently, a new PolSAR architecture called the Hybrid-Polarity (HP) architecture has attracted worldwide attentions.Compared with conventional linearly-polarized PolSARs, HP architecture based PolSARs have significant advantages such as wider swath coverage and lower hardware requirement.In this paper, the principles of the HP architecture, including system designs, system models and calibration methods are first reviewed.Two implementation difficulties of the HP architecture, concerning calibration issue and transmit configuration are illustrated.In order to overcome these problems, an improved version of the HP architecture is proposed.A prototype system based on this improved HP architecture developed for experimental validation is also introduced.In the latter part of this paper, applications suitable for the HP architecture based PolSARs are reviewed.Since the quadrature-polarimetric (quad-pol) data provided by an HP architecture based PolSAR system may be directly transformed into conventional linearly-polarized quad-pol data, this part of review is mainly focused on the corresponding dual-pol applications, i.e.Compact Polarimetry (CP) applications.
2016, 5(6): 596-606.
Synthetic Aperture Radar (SAR), an important earth observation sensor, has been used in a wide range of applications for land and marine surveillance.Polarimetric SAR (PolSAR) can obtain abundant scattering information of a target to improve the ability of target detection, classification, and quantitative inversion.In this paper, the important role of PolSAR in ocean monitoring is discussed with factors such as sea ice, ships, oil spill, waves, internal waves, and seabed topography.Moreover, the future development direction of PolSAR is put forward to get an inspiration for further research of PolSAR in marine surveillance applications.
Synthetic Aperture Radar (SAR), an important earth observation sensor, has been used in a wide range of applications for land and marine surveillance.Polarimetric SAR (PolSAR) can obtain abundant scattering information of a target to improve the ability of target detection, classification, and quantitative inversion.In this paper, the important role of PolSAR in ocean monitoring is discussed with factors such as sea ice, ships, oil spill, waves, internal waves, and seabed topography.Moreover, the future development direction of PolSAR is put forward to get an inspiration for further research of PolSAR in marine surveillance applications.
2016, 5(6): 607-619.
Spaceborne Compact Polarimetric Synthetic Aperture Radar (CP SAR) is a new form of SAR, which has intrinsic advantages in maritime surveillance because it can obtain relatively rich polarimetric information of targets with wide swath.First, the basic modes and the development of a spaceborne CP SAR system are introduced in this paper with respect to ship detection applications.Second, typical methods of spaceborne CP SAR information processing are reviewed.Third, the attributes of frequently used methods for spaceborne CP SAR ship detection are analyzed and compared in depth.Fourth, the results of our research on spaceborne CP SAR ship detection are given.Finally, suggestions for further research on spaceborne CP SAR ship detection are proposed.
Spaceborne Compact Polarimetric Synthetic Aperture Radar (CP SAR) is a new form of SAR, which has intrinsic advantages in maritime surveillance because it can obtain relatively rich polarimetric information of targets with wide swath.First, the basic modes and the development of a spaceborne CP SAR system are introduced in this paper with respect to ship detection applications.Second, typical methods of spaceborne CP SAR information processing are reviewed.Third, the attributes of frequently used methods for spaceborne CP SAR ship detection are analyzed and compared in depth.Fourth, the results of our research on spaceborne CP SAR ship detection are given.Finally, suggestions for further research on spaceborne CP SAR ship detection are proposed.
2016, 5(6): 620-638.
As one of the topical research area in the field of radar, polarimetric signal processing techniques gradually receive the attention of scholars worldwide and have been widely applied in various fields.The basis of polarimetric signal processing is to acquire polarization information.In this paper, the research statuses of several relevant key aspects are reviewed, including polarization information acquisition, polarization diversity and coding, polarization anti-interference/clutter, polarization detection, and classification and identification of targets.Finally, the problems faced by radar polarimetry techniques are concluded, and the prospects of future development of the techniques are discussed.
As one of the topical research area in the field of radar, polarimetric signal processing techniques gradually receive the attention of scholars worldwide and have been widely applied in various fields.The basis of polarimetric signal processing is to acquire polarization information.In this paper, the research statuses of several relevant key aspects are reviewed, including polarization information acquisition, polarization diversity and coding, polarization anti-interference/clutter, polarization detection, and classification and identification of targets.Finally, the problems faced by radar polarimetry techniques are concluded, and the prospects of future development of the techniques are discussed.
2016, 5(6): 639-646.
Whole space polarimetric bistatic scattering data of full-size aircraft targets were calculated via the mature electromagnetic calculation software.The fluctuation statistics characteristic of the polarimetric bistatic Radar Cross-Section (RCS) was carried out.It was found that the statistical properties of the four polarimetric types (HH, HV, VH, VV) of polarimetric bistatic RCSs are nearly the same, while the monostatic main and cross polarization RCSs statistical properties were quite different from each other.The characteristics of the distribution statistic for the monostatic and bistatic polarization ratio were carried out.Moreover, it was found that the cross-main polarization ratios were quite different, while the main polarization ratios were similar.The statistical results provide a theoretical reference for fully polarimetric bistatic radar aircraft target detection experiments.
Whole space polarimetric bistatic scattering data of full-size aircraft targets were calculated via the mature electromagnetic calculation software.The fluctuation statistics characteristic of the polarimetric bistatic Radar Cross-Section (RCS) was carried out.It was found that the statistical properties of the four polarimetric types (HH, HV, VH, VV) of polarimetric bistatic RCSs are nearly the same, while the monostatic main and cross polarization RCSs statistical properties were quite different from each other.The characteristics of the distribution statistic for the monostatic and bistatic polarization ratio were carried out.Moreover, it was found that the cross-main polarization ratios were quite different, while the main polarization ratios were similar.The statistical results provide a theoretical reference for fully polarimetric bistatic radar aircraft target detection experiments.
2016, 5(6): 647-657.
Knowledge of target polarization characteristics is valuable for radar target detection, classification, and identification.We conducted experimental research on an Unmanned Aerial Vehicle (UAV) with complex materials and structures to determine the differences in polarimetric scattering between the UAV and its perfect electric conductor model.To illustrate the coherence of the entire UAV and its components using polarimetric scattering, we measured and analyzed each part.The results reveal that the airframe and aerofoils directly influence the depolarization, and that the polarimetric scattering characteristics of the airframe represent the primary source for the whole UAV.
Knowledge of target polarization characteristics is valuable for radar target detection, classification, and identification.We conducted experimental research on an Unmanned Aerial Vehicle (UAV) with complex materials and structures to determine the differences in polarimetric scattering between the UAV and its perfect electric conductor model.To illustrate the coherence of the entire UAV and its components using polarimetric scattering, we measured and analyzed each part.The results reveal that the airframe and aerofoils directly influence the depolarization, and that the polarimetric scattering characteristics of the airframe represent the primary source for the whole UAV.
2016, 5(6): 658-665.
Salisbury screens have a number of unique electromagnetic scattering characteristics.When appropriately designed, the Salisbury screen can reach the radar target signature transform.Based on the electromagnetic scattering characteristics of the Salisbury screen, we designed a novel dihedral corner, and theoretically analyzed and simulated its electromagnetic scattering characteristics in this study.The results reveal the monostatic radar cross section curves of the 90nd 60 Salisbury screen dihedral and metal dihedral, respectively.Taking an orthogonal dihedral corner as an example, we obtained the polarization scattering matrixes for different incident degrees.In addition, we investigated the influence of illumination frequency, target gestures, and other key factors on the polarization characteristics of the Salisbury screen dihedral corner.The theoretical and simulation analysis results show that compared with the conventional metal dihedral corner, the Salisbury screen dihedral corner significantly influences the scattering characteristics and will have potential application in electronic warfare.
Salisbury screens have a number of unique electromagnetic scattering characteristics.When appropriately designed, the Salisbury screen can reach the radar target signature transform.Based on the electromagnetic scattering characteristics of the Salisbury screen, we designed a novel dihedral corner, and theoretically analyzed and simulated its electromagnetic scattering characteristics in this study.The results reveal the monostatic radar cross section curves of the 90nd 60 Salisbury screen dihedral and metal dihedral, respectively.Taking an orthogonal dihedral corner as an example, we obtained the polarization scattering matrixes for different incident degrees.In addition, we investigated the influence of illumination frequency, target gestures, and other key factors on the polarization characteristics of the Salisbury screen dihedral corner.The theoretical and simulation analysis results show that compared with the conventional metal dihedral corner, the Salisbury screen dihedral corner significantly influences the scattering characteristics and will have potential application in electronic warfare.
2016, 5(6): 666-672.
This paper focuses on the countermeasures of airborne towed radar active decoy.Moreover, a detection and suppression scheme of Towed Radar Active Decoy (TRAD) using polarization information is proposed.A full-polarization radar echo model with the presence of jamming is established.Furthermore, based on a monopulse radar angle measurement system, the difference between the characteristics of TRAD and radar targets in different polarization channels is analyzed.A detection scheme is proposed using the differences of target Polarization Scattering Matrix (PSM) divergence with the presence and absence of TRAD.Subsequently, the corresponding jamming suppression algorithm is developed.The efficiency and advantages of the proposed algorithm are validated via theoretical analyses and simulation studies.This paper provides an effective method to detect TRAD and can provide a significant reference for improving the precision strike of terminal guidance radar under jamming.
This paper focuses on the countermeasures of airborne towed radar active decoy.Moreover, a detection and suppression scheme of Towed Radar Active Decoy (TRAD) using polarization information is proposed.A full-polarization radar echo model with the presence of jamming is established.Furthermore, based on a monopulse radar angle measurement system, the difference between the characteristics of TRAD and radar targets in different polarization channels is analyzed.A detection scheme is proposed using the differences of target Polarization Scattering Matrix (PSM) divergence with the presence and absence of TRAD.Subsequently, the corresponding jamming suppression algorithm is developed.The efficiency and advantages of the proposed algorithm are validated via theoretical analyses and simulation studies.This paper provides an effective method to detect TRAD and can provide a significant reference for improving the precision strike of terminal guidance radar under jamming.
2016, 5(6): 673-680.
High Frequency Surface Wave Radar (HFSWR) is able to receive surface target and low-flying aircraft echoes at a long-distance, but it suffers severely from ionospheric clutter.In this paper, a spacepolarization collaborative-based filter is introduced to mitigate ionospheric clutter.For parameter estimation on ionospheric clutter used for filters, a spatial parameter estimation algorithm based on compressive sensing is introduced to the DOA estimation of ionospheric clutter.In addition, a polarized parameter estimation algorithm based on statistical characteristics is proposed for ionospheric clutter in the range-Doppler spectrum.Higher estimation accuracy is achieved as a result of the range-Doppler spectrum;therefore, these two estimation algorithms enhance the performance of the space-polarization collaborative suppression method for ionospheric clutter.Experimental results of practical dual-polarized HFSWR data show the effectiveness of the two algorithms and the above mentioned filter for ionospheric clutter suppression.
High Frequency Surface Wave Radar (HFSWR) is able to receive surface target and low-flying aircraft echoes at a long-distance, but it suffers severely from ionospheric clutter.In this paper, a spacepolarization collaborative-based filter is introduced to mitigate ionospheric clutter.For parameter estimation on ionospheric clutter used for filters, a spatial parameter estimation algorithm based on compressive sensing is introduced to the DOA estimation of ionospheric clutter.In addition, a polarized parameter estimation algorithm based on statistical characteristics is proposed for ionospheric clutter in the range-Doppler spectrum.Higher estimation accuracy is achieved as a result of the range-Doppler spectrum;therefore, these two estimation algorithms enhance the performance of the space-polarization collaborative suppression method for ionospheric clutter.Experimental results of practical dual-polarized HFSWR data show the effectiveness of the two algorithms and the above mentioned filter for ionospheric clutter suppression.
2016, 5(6): 681-691.
The decision tree model has great significance in the application of polarimetric SAR data classification, whose results in many types of classification applications obtain good accuracy and are interpretable by polarimetric scattering mechanisms.In the traditional decision tree model, because one single feature is employed by the nodes of the decision tree, the accuracy of the classification result tends to be poor, especially, for applications that classify objects with similar scattering characteristics.In this paper, we propose an improved method to create a two-dimensional vector of features instead of one single feature at the decision nodes.As a result, the classification results of the new method adopting the same feature set as the traditional decision tree can achieve better accuracy.In addition, after classification, the new method may employ a confusion matrix to identify the decision node that yields a classification error, which will facilitate the objectoriented feedback adjustment of classification results, thus making it possible to improve the classification accuracy of the specified object.Our experimental results with AIRSAR-Flevoland data prove the validity of the proposed method, and we draw some useful conclusions about the scattering characteristics of several types of vegetation.
The decision tree model has great significance in the application of polarimetric SAR data classification, whose results in many types of classification applications obtain good accuracy and are interpretable by polarimetric scattering mechanisms.In the traditional decision tree model, because one single feature is employed by the nodes of the decision tree, the accuracy of the classification result tends to be poor, especially, for applications that classify objects with similar scattering characteristics.In this paper, we propose an improved method to create a two-dimensional vector of features instead of one single feature at the decision nodes.As a result, the classification results of the new method adopting the same feature set as the traditional decision tree can achieve better accuracy.In addition, after classification, the new method may employ a confusion matrix to identify the decision node that yields a classification error, which will facilitate the objectoriented feedback adjustment of classification results, thus making it possible to improve the classification accuracy of the specified object.Our experimental results with AIRSAR-Flevoland data prove the validity of the proposed method, and we draw some useful conclusions about the scattering characteristics of several types of vegetation.
2016, 5(6): 692-700.
In this paper, we propose a supervised classification algorithm for Polarimetric Synthetic Aperture Radar (PolSAR) images using multiple-feature fusion and ensemble learning.First, we extract different polarimetric features, including extended polarimetric feature space, Hoekman, Huynen, H/alpha/A, and fourcomponent scattering features of PolSAR images.Next, we randomly select two types of features each time from all feature sets to guarantee the reliability and diversity of later ensembles and use a support vector machine as the basic classifier for predicting classification results.Finally, we concatenate all prediction probabilities of basic classifiers as the final feature representation and employ the random forest method to obtain final classification results.Experimental results at the pixel and region levels show the effectiveness of the proposed algorithm.
In this paper, we propose a supervised classification algorithm for Polarimetric Synthetic Aperture Radar (PolSAR) images using multiple-feature fusion and ensemble learning.First, we extract different polarimetric features, including extended polarimetric feature space, Hoekman, Huynen, H/alpha/A, and fourcomponent scattering features of PolSAR images.Next, we randomly select two types of features each time from all feature sets to guarantee the reliability and diversity of later ensembles and use a support vector machine as the basic classifier for predicting classification results.Finally, we concatenate all prediction probabilities of basic classifiers as the final feature representation and employ the random forest method to obtain final classification results.Experimental results at the pixel and region levels show the effectiveness of the proposed algorithm.
2016, 5(6): 701-710.
Conventional distributed-target-based polarimetric calibration algorithms estimate polarimetric distortions by assuming that the measured spatially averaged covariance matrix takes a specific form.However, when the underlying surface contains targets that do not satisfy the assumptions employed by those algorithms, the averaged covariance matrix may deviate from the desired form.As a result, poor estimates of distortion parameters may yield.It is known that spherically truncated covariance matrix is robust to outliers.Thus, we introduce it to the polarimetric SAR calibration routine.Experiment results on the airborne SAR data confirm that this method can effectively reduce the uncertainty of distortion estimates, hence improve the robustness of the calibration.
Conventional distributed-target-based polarimetric calibration algorithms estimate polarimetric distortions by assuming that the measured spatially averaged covariance matrix takes a specific form.However, when the underlying surface contains targets that do not satisfy the assumptions employed by those algorithms, the averaged covariance matrix may deviate from the desired form.As a result, poor estimates of distortion parameters may yield.It is known that spherically truncated covariance matrix is robust to outliers.Thus, we introduce it to the polarimetric SAR calibration routine.Experiment results on the airborne SAR data confirm that this method can effectively reduce the uncertainty of distortion estimates, hence improve the robustness of the calibration.
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